U.S. patent application number 15/269901 was filed with the patent office on 2017-03-23 for optical fingerprint sensor package.
The applicant listed for this patent is Synaptics Incorporated. Invention is credited to Jason Goodelle, Chien Lam, Young Seen Lee, Bob Lee Mackey, Paul Wickboldt.
Application Number | 20170083745 15/269901 |
Document ID | / |
Family ID | 58283040 |
Filed Date | 2017-03-23 |
United States Patent
Application |
20170083745 |
Kind Code |
A1 |
Goodelle; Jason ; et
al. |
March 23, 2017 |
OPTICAL FINGERPRINT SENSOR PACKAGE
Abstract
Disclosed are optical sensors, optical fingerprint sensor
packages, and methods for forming same. An optical sensor
comprises: a substrate; an image sensor disposed over the
substrate; a light source disposed over the substrate; a light
guide disposed over the image sensor; and, an encapsulant disposed
over the light source, wherein the encapsulant is coupled to the
light guide and comprises a surface positioned to reflect light
emitted from the light source and direct the reflected light into
the light guide.
Inventors: |
Goodelle; Jason; (San Jose,
CA) ; Wickboldt; Paul; (Walnut Creek, CA) ;
Lee; Young Seen; (Newark, CA) ; Lam; Chien;
(San Jose, CA) ; Mackey; Bob Lee; (San Jose,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Synaptics Incorporated |
San Jose |
CA |
US |
|
|
Family ID: |
58283040 |
Appl. No.: |
15/269901 |
Filed: |
September 19, 2016 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
62220712 |
Sep 18, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G06K 9/00053 20130101;
H01L 2224/48091 20130101; H01L 2924/00012 20130101; H01L 2924/00014
20130101; H01L 2924/181 20130101; H01L 2224/48227 20130101; H01L
2924/181 20130101; H01L 2224/73265 20130101; H01L 2224/48091
20130101; G06K 9/0004 20130101 |
International
Class: |
G06K 9/00 20060101
G06K009/00 |
Claims
1. An optical sensor, comprising: a substrate; an image sensor
disposed over the substrate; a light source disposed over the
substrate; a light guide disposed over the image sensor; and an
encapsulant disposed over the light source, wherein the encapsulant
is coupled to the light guide and comprises a surface positioned to
reflect light emitted from the light source and direct the
reflected light into the light guide.
2. The optical sensor of claim 1, wherein the substrate comprises a
package substrate having electrical interconnections, wherein the
image sensor is electrically connected to the package substrate,
and wherein the light source is electrically connected to the
package substrate.
3. The optical sensor of claim 1, wherein the image sensor
comprises a photodetector array.
4. The optical sensor of claim 1, wherein the image sensor
comprises a semiconductor die attached to the substrate.
5. The optical sensor of claim 1, wherein the image sensor is
disposed over a first area of the substrate, and wherein the light
source is disposed over a second area of the substrate outside of
the first area of the substrate.
6. The optical sensor of claim 1, wherein the light source
comprises a light-emitting diode (LED) attached to the
substrate.
7. The optical sensor of claim 1, wherein the light source
comprises a plurality of light-emitting diodes (LEDs) disposed over
the substrate on opposing sides of the image sensor.
8. The optical sensor of claim 1, wherein the encapsulant comprises
an optically clear molding compound.
9. The optical sensor of claim 1, wherein the encapsulant and the
light guide are integrally formed, wherein the encapsulant and the
light guide comprise an optically clear molding compound.
10. The optical sensor of claim 1, further comprising: an air gap
disposed over the image sensor and disposed between the light guide
and the image sensor.
11. The optical sensor of claim 1, further comprising: a light
filter disposed over the image sensor and disposed between the
light guide and the image sensor.
12. The optical sensor of claim 11, further comprising: an air gap
disposed over the light filter and disposed between the light guide
and the light filter.
13. The optical sensor of claim 11, wherein the light filter
comprises a collimator filter.
14. The optical sensor of claim 1, further comprising: a reflective
layer disposed over the encapsulant.
15. The optical sensor of claim 14, wherein the reflective layer
comprises a metallic coating over the surface positioned to reflect
light, and wherein the metallic coating comprises a window in an
area over the light guide and over an active area of the image
sensor.
16. The optical sensor of claim 1, wherein the surface of the
encapsulant is configured to reflect the light using Fresnel
reflection.
17. The optical sensor of claim 1, wherein the surface of the
encapsulant comprises a flat surface that is tilted relative to the
light source.
18. The optical sensor of claim 1, wherein the surface of the
encapsulant comprises a curved surface.
19. An optical fingerprint sensor package, comprising: a package
substrate; an image sensor die disposed over the package substrate,
wherein the image sensor die comprises a photodetector array and is
electrically connected to the package substrate; a light filter
disposed over the image sensor die; a light-emitting diode (LED)
light source disposed over the package substrate; a light guide
disposed over the light filter; an air gap disposed over the light
filter between the light guide and the light filter; and an
optically clear molding compound disposed over the LED light
source, wherein the optically clear molding compound is coupled to
the light guide and comprises a surface positioned to reflect light
emitted from the light source and direct the reflected light into
the light guide.
20. The optical fingerprint sensor package of claim 19, wherein the
light filter comprises a collimator filter, wherein the collimator
filter is configured to transmit a set of incident light rays
within an acceptance angle from a normal to the collimator filter,
and wherein the collimator filter is configured to reject a set of
incident light rays outside of an acceptance angle from the normal
to the collimator filter.
21. An optical fingerprint sensor package, comprising: a package
substrate; an image sensor die disposed over the package substrate,
wherein the image sensor die comprises a photodetector array and is
electrically connected to the package substrate; a light-emitting
diode (LED) light source disposed over the package substrate; and
an optically clear molding compound disposed over the LED light
source, wherein the optically clear molding compound is coupled to
the light guide and comprises a surface positioned to reflect light
emitted from the light source and direct the reflected light to a
sensing area above the image sensor die.
22. A method of forming an optical sensor package, the method
comprising: attaching an image sensor die to a substrate;
electrically connecting the image sensor die to the substrate;
mounting a light-emitting diode (LED) to the substrate; and
overmolding the LED with an optically clear molding compound,
wherein a light guide is disposed over the image sensor die, and
wherein the optically clear molding compound comprises a surface
positioned to reflect light emitted from the LED and direct the
reflected light into the light guide.
23. The method of claim 22, wherein the image sensor die is
electrically connected to the substrate by wire bonding the image
sensor die to the substrate.
24. The method of claim 22, wherein the image sensor die is
attached to the substrate and electrically connected to the
substrate by flip chip attaching the image sensor die to the
substrate.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. provisional patent
application number 62/220,712, filed on Sep. 18, 2015, the entire
contents of which is hereby incorporated by reference in its
entirety.
FIELD
[0002] The present disclosure generally relates to optical sensors
and, more specifically, to packaging for optical fingerprint
sensors.
SUMMARY
[0003] In one aspect, an optical sensor comprises: a substrate; an
image sensor disposed over the substrate; a light source disposed
over the substrate; a light guide disposed over the image sensor;
and, an encapsulant disposed over the light source, wherein the
encapsulant is coupled to the light guide and comprises a surface
positioned to reflect light emitted from the light source and
direct the reflected light into the light guide.
[0004] In another aspect, an optical fingerprint sensor package
comprises: a package substrate; an image sensor die disposed over
the package substrate, wherein the image sensor die comprises a
photodetector array and is electrically connected to the package
substrate; a light filter disposed over the image sensor die; a
light-emitting diode (LED) light source disposed over the package
substrate; a light guide disposed over the light filter; an air gap
disposed over the light filter between the light guide and the
light filter; and, an optically clear molding compound disposed
over the LED light source, wherein the optically clear molding
compound is coupled to the light guide and comprises a surface
positioned to reflect light emitted from the light source and
direct the reflected light into the light guide.
[0005] In another aspect, an optical fingerprint sensor package
comprises: a package substrate; an image sensor die disposed over
the package substrate, wherein the image sensor die comprises a
photodetector array and is electrically connected to the package
substrate; a light-emitting diode (LED) light source disposed over
the package substrate; and, an optically clear molding compound
disposed over the LED light source, wherein the optically clear
molding compound is coupled to the light guide and comprises a
surface positioned to reflect light emitted from the light source
and direct the reflected light to a sensing area above the image
sensor die.
[0006] In another aspect, a method of forming an optical sensor
package comprises: attaching an image sensor die to a substrate;
electrically connecting the image sensor die to the substrate;
mounting a light-emitting diode (LED) to the substrate; and,
overmolding the LED with an optically clear molding compound,
wherein a light guide is disposed over the image sensor die, and
wherein the optically clear molding compound comprises a surface
positioned to reflect light emitted from the LED and direct the
reflected light into the light guide.
BACKGROUND
[0007] Input devices, including proximity sensor devices (such as
touchpad and touch screen sensor devices) and biometric sensor
devices (such as fingerprint sensor and eye scanner devices), are
widely used in a variety of electronic systems. A sensor device
typically includes a sensing region, often demarked by a surface,
in which the sensor device detects one or more input objects to
determine positional information and/or image the input object.
Sensor devices may be used to provide interfaces for the electronic
system. For example, sensor devices are often used as input devices
for larger computing systems (such as notebook and desktop
computers) and smaller computing systems (such as cellular phones
and wearable computing devices) to provide interfaces for control
inputs and user authentication.
[0008] Input devices utilizing optical sensors sometimes
incorporate active illumination of the input object (e.g., a
finger). These typically require additional auxiliary light sources
that add to the cost and complexity of the device design and
assembly.
BRIEF DESCRIPTION OF DRAWINGS
[0009] The exemplary embodiments of the present disclosure will
hereinafter be described in conjunction with the appended drawings,
where like designations denote like elements.
[0010] FIGS. 1A-1C depict wire bonded optical sensor packages.
[0011] FIGS. 2A-2B depict a plurality of optical sensor packages in
a panel or array format.
[0012] FIG. 3 depicts an optical sensor package having a reflective
layer.
[0013] FIGS. 4A-4B depict a flip chip attached optical sensor
package.
[0014] FIG. 5 depicts an optical sensor package having an
encapsulant over an LED (light-emitting diode) light source, and a
light guide separate from the encapsulant.
[0015] FIG. 6 depicts an optical sensor package having reflector
structures attached to a substrate.
[0016] FIG. 7 depicts an optical sensor package having an air gap
above an image sensor die and below an optically clear cover or
light guide.
[0017] FIGS. 8A-8B depict an optical sensor package having a
lid.
[0018] FIG. 8C depicts a lid array that can be attached to a
substrate.
[0019] FIGS. 9A-9B depict an optical sensor package having an
optically clear mold applied to opposing sides of a substrate.
[0020] FIGS. 10A-10B depict an optical sensor package having a
curved reflecting surface.
[0021] FIG. 11 depicts an optical sensor package mounted underneath
a display cover glass.
[0022] FIGS. 12A-12B depict methods of making optical sensor
packages.
DETAILED DESCRIPTION
[0023] The following detailed description is merely exemplary in
nature and is not intended to limit the embodiments or the
application and uses of the embodiments. Furthermore, there is no
intention to be bound by any expressed or implied theory presented
in the preceding technical field, background, summary, or the
following detailed description.
[0024] Turning now to the figures, FIGS. 1A-1B depict an optical
fingerprint sensor package 101a in which a front side illuminated
(FSI) image sensor die 103 is connected to a substrate 105 using
wire bonds 107. FIG. 1A depicts the optical fingerprint sensor
package 101a in cross-section view, while FIG. 1B depicts the
optical fingerprint sensor package 101a in isometric view.
[0025] In the optical fingerprint sensor package 101a, the image
sensor die 103 is positioned over the substrate 105 and attached to
the substrate 105 using a die attach layer 115. The die attach
layer 115 attaches or bonds the image sensor die 103 to the
substrate 105 and may include any suitable die attach material,
with adhesives such as epoxy or solder being some examples. The
image sensor die 103 is electrically connected to the substrate
using wire bonds 107 connected to a peripheral portion of the die.
In this example, the image sensor die 103 is a FSI image sensor and
the wire bonds 107 are bonded to the active side of the die, which
also corresponds to an upper surface or upper side of the die in
this orientation. The substrate 105 is any suitable electronic
package or integrated circuit (IC) package substrate that provides
routing or electrical interconnections for connecting the image
sensor die 103 to external devices. The image sensor die 105
includes a plurality of light sensitive elements or a photodetector
array for optically capturing a fingerprint image from a sensing
region over the image sensor die 103 and optical fingerprint sensor
package 101a. In FIG. 1A, the sensing region or sensing side
corresponds to the upper side of the package and the upper side of
the figure.
[0026] A light filter 117 or optical element layer is positioned
over the image sensor die 103. The light filter 117 conditions or
filters the light reaching the photodetector array of the image
sensor die 103 to capture a suitable fingerprint image. The light
filter 117 may include a collimator filter that filters incident
light so that only rays of light that are within an acceptance
angle from normal to the collimator filter plane are transmitted or
allowed to pass through the collimator filter, while the collimator
filter rejects or blocks rays of light that are outside of the
acceptance angle. That is, the collimator filter transmits incident
light whose rays of light are parallel to the normal of the
collimator filter plane (which is also the normal of the image
sensor plane), and the collimator filter also transmits a set of
rays that are not perfectly parallel but within a given acceptance
angle relative to that normal, but the collimator filter blocks a
set of rays that are outside of the given acceptance angle relative
to normal. The acceptance angle of the collimator filter may vary
depending on the desired image resolution, sensing distance, or
other parameters. In alternate implementations, the light filter
117 may include other optical elements for acting on the light
reaching the image sensor die 103, such as lenses, pinholes,
diffractive elements (e.g., zone plates), or optical fiber bundles.
The light filter 117 may optionally be fabricated or manufactured
using wafer level processing in connection with the wafer
processing of the image sensor dies.
[0027] The optical fingerprint sensor package 101a also includes a
plurality of LED light sources 119 positioned over the substrate
105 in areas outside of the sensor die area and next to the image
sensor die 103. Multiple LED light sources 119 are included on
opposing sides of the image sensor die 103. In this example, four
LED light sources 119 are included, two on one side of the image
sensor die 103 and two on the opposite side of the image sensor die
103. The LED light sources 119 include upward firing LEDs that may
be soldered or otherwise attached to the substrate 105. An
optically clear epoxy molding compound (OCEMC) 121 is positioned
over the LED light sources 119 and provides an encapsulant over the
LED light sources 119. The OCEMC 121 also extends over the sensing
area (corresponding to the active area of the image sensor die 103)
forming a light guide 122a in this sensing area that is integral
with and optically coupled to the portion of OCEMC that is
positioned over the LED light sources 119. The light guide 122a can
be used to direct light emitted from the LED light sources 119
towards a sensing region or an input object, such as a finger, that
is positioned over the sensing area. The OCEMC 121 includes an
internally reflecting surface 123 in an area over or proximate to
the LED light source 119 that is positioned to reflect light
emitted from the LED light source 119 and direct the reflected
light into the light guide 122a at an angle that creates total
internal reflection in the light guide 122a.
[0028] The OCEMC 121 over the LED light sources 119 is transparent
to the light emitted by the LEDs to a sufficient degree to allow
the light from the LEDs to pass therethrough and reach the sensing
region above the image sensor die 103. In this example, the OCEMC
also surrounds the image sensor die 103 and encapsulates the image
sensor die 103 as well, including the wire bonds 107. The OCEMC 121
has an index of refraction greater than that of air (or another
medium outside the OCEMC 121 surface 123 boundary, depending on the
construction or operating environment), which may vary depending on
the particular choice of material. An example refractive index for
the OCEMC is about 1.5, but this may vary in different
implementations depending on the choice of material used. The
refractive index of the OCEMC 121 relative to the surrounding
environment (e.g., air) allows the light emitted by the LED light
sources 119 to reflect at the surface 123 using Fresnel reflection.
This may be achieved by positioning the reflecting surface 123
relative to the LED light source 119 such that a portion of the
light emitted by the LED is incident at this surface 123 at the
critical angle determined by this interface and directed to the
desired sensing area. In optical fingerprint sensor package 101a,
this is achieved by having a tilted or beveled surface with a flat
geometry that is angled relative to the LEDs to reflect light
incident at the surface 123 in this manner and direct this light
into the light guide 122a. It will be appreciated that the
particular angle or angles to achieve this effect may vary in
different implementations.
[0029] The substrate 105 provides an interposer with electrical
interconnections, routing, or wiring for electrically connecting
the image sensor die 103 and LED light sources 119 to other
components. The optical fingerprint sensor package 101a of FIGS.
1A-1B includes a connector 109 and a flex tail 111 (i.e., flexible
connector) that are electrically connected to the substrate 105.
FIG. 1C depicts a cross-section view of optical fingerprint sensor
package 101b, which is similar to the optical fingerprint sensor
package 101a shown in FIGS. 1A-1B, except in this implementation
ball grid array (BGA) balls 113 are electrically connected to the
substrate 105. The flexible connector 111 or BGA balls 113 can be
used to connect the sensor package to external devices or circuitry
(not pictured), and it will be appreciated that other interconnects
may be suitable as well. The optical modules in FIGS. 1A-1C could
include other components besides the CMOS (complementary
metal-oxide-semiconductor) image sensor and LEDs, such as passive
components, other control chips, and the like. The finished module
depends on exact product or application parameters. However, it is
possible for all components to be included within the same package
(either within or outside the OCEMC region) in various
implementations.
[0030] FIGS. 2A-2B depict a panel or strip level processing format
that can be applied to the optical FPS package assembly flow for
the optical fingerprint sensor packages 101a from FIGS. 1A-1B. FIG.
2A depicts a top view or plan view of multiple optical fingerprint
sensor packages 101a in a panel or strip before singulation of the
individual sensor packages, while FIG. 2B depicts the optical
fingerprint sensor packages 101a in isometric view. By utilizing
panel or strip level processing, lower cost and smaller form factor
devices can be realized. Fabricating the optical FPS packages can
be completed using standard panel level (or strip level) processes
using a continuous molded section through all the individual
optical fingerprint sensor packages 101a, and the individual
optical fingerprint sensor packages 101a can be subsequently
singulated using a variety of techniques such as mechanical blade
saw or laser dicing along singulation lines 137, as an example.
While the example in FIGS. 2A-2B uses the optical fingerprint
sensor package 101a from FIGS. 1A-1B, the panel, strip, or array
processing format can be applied to other packages described
herein. Board level attachment of the optical FPS package can be
realized by implementing standard 2nd level interconnects such as
flex circuits and BGA balls for example.
[0031] FIG. 3 depicts another optical fingerprint sensor package
101c. The optical fingerprint sensor package 101c includes a
reflective layer 131 positioned over the reflection surface 123 to
provide or enhance reflection of light emitted by the LEDs. The
reflective layer 131 includes a window 133 over an active area or
sensing area of the image sensor die 103 to permit light sensed
from a finger or other object to reach the detector elements of the
image sensor die 103. The reflective layer 131 may be formed by
coating a metallic film on an outer surface of the OCEMC 121,
particularly on the angled surface 123, while leaving the sensing
area exposed or free of the reflective metallic film. This coating
can be applied using masking techniques and commercially available
metal sputtering or plating. Aluminum (Al), silver (Ag), gold (Au),
and Nickel (Ni) films are examples of materials that can be used in
the reflective layer, and they can be applied after panel molding,
e.g., such as that shown in FIGS. 2A-2B.
[0032] FIGS. 4A-4B depict another optical fingerprint sensor
package 101d. While FIGS. 1A-1C depict a wire bonded solution,
FIGS. 4A-4B shows the use of a complementary
metal-oxide-semiconductor (CMOS) image sensor die 103 (in this case
a back side illumination type) that utilizes through silicon via
(TSV) technology plus flip chip attach technology (e.g, Cu pillar
bumps, solder bumps, etc.) to attach and electrically connect the
image sensor die 103 to the substrate 105. The flip chip solution
that can help reduce the form factor (coupled with panel or strip
level assembly) by eliminating the need for wire bonds around the
periphery of the die to make electrical connections. It is
estimated that this can save .about.300 to 500 um in package size
in x,y dimensions, depending on the flip chip process. Underfill
139 is used in this example, as is typically used along with a flip
chip die attach process, but the underfill may be eliminated by the
use of an overmold material with appropriate material properties
(typically known as molded underfill or "MUF").
[0033] FIG. 5 depicts another optical sensor package 101e. The
optical sensor package 101e includes a light guide 122b that is
separate from the OCEMC 121, and that is positioned over the image
sensor die 103 and light filter 117. The light guide 122b includes
an optically clear layer that is optically coupled to the OCEMC
121. In this case, the light guide 122b is optically coupled to the
separate OCEMC layer 121 by positioning these two layers in contact
with each other. The light guide 122b layer may be wafer level
applied on top of the light filter layer. This light guide layer
may also be applied by laminating to the surface of the wafer. The
light guide 122b layer may be applied prior to packaging by using
wafer level applied (or laminated) optically clear illumination
layer(s) formed directly on top of the light filter 117. Improved
performance may be realized by reducing trapped open spaces and
providing better light guiding performance. This may be a more
costly approach in some instances, but may allow for more
flexibility in fabrication modes (for example to laminate a layer
that contains microstructures for a higher performance light guide
illumination layer).
[0034] FIG. 6 depicts another optical sensor package 101f. The
optical sensor package 101f includes reflector structures that can
be strategically placed on the substrate 105 prior to overmolding
or encapsulation to enhance the amount light entering the light
guide 122a. In this example, the reflector structures are
positioned between the LED light source 119 and the image sensor
die 103. The LED light sources 119 may emit light at a wide angle
that disperses in multiple directions, including straight up,
towards the outer portion of the package, and towards the inner
portion of the package. The reflector structures 141 are positioned
to reflect the light that is emitted towards the inner portion of
the package back towards the reflecting surface 123, where it can
be further reflected towards the light guide 122a. Multiple
reflection structures are included in this example, but more or
fewer may be used. For example, a single reflection structure 141
may be included if only a single LED is included in the package.
These structures can be overmolded with OCEMC during the same
process used to encapsulate the other structures.
[0035] FIG. 7 depicts another optical sensor package 101g. The
optical sensor package 101g includes an air gap 143. The air gap
143 is below the light guide 122a and above the light filter 117,
and the air gap 143 may be molded in, in this example. In
alternative implementations, the air gap 143 may be replaced with a
low refractive index material having a lower refractive index than
the light guide 122a.
[0036] FIGS. 8A-8B depict another optical sensor package 101h. The
optical sensor package 101h includes an optically clear lid 151 or
cap positioned over the image sensor die 103. The lid 151 provides
a protective cover and a light guide 122a over the image sensor die
103, with an air gap 143 below the light guide, between the light
guide and the light filter layer 117. The lid 151 also provides an
air cavity 153 around the image sensor die 103 and over the wire
bonds 107. This construction protects the CMOS image sensor, any
passives or other components, and wirebonds using "no contact,"
while still providing a light guide solution. The lid 151 can be
made of an optically clear epoxy molding compound or other
materials, and can be placed directly on top of pre-mounted LEDs.
The lid 151 also includes reflective surface 123 over the LED light
source 119. Coupling adhesives or fluids can be used to improve the
light coupling between the pre-mounted LEDs and the clear lid or
cap. Also, optical sensor package 101h can make use of pre-molded
clear lids that can be applied to the substrate 105 in panel form,
with the image sensor and other components already mounted in
matrix (array) form. This is shown in FIG. 8C. The lid array 251
can be adhesively bonded to the substrate panel 205 and can be
subsequently singulated using mechanical or other means. This
format allows for low cost and ease of fabrication of the lid array
and allows for a potentially favorable non-contact (i.e., no
contact with CMOS image sensor) geometry. Also, the use of low
modulus adhesives to attach the lid arrays to the substrate could
be employed to provide a mechanical buffer between the typically
high coefficient of thermal expansion (CTE) optically clear lid and
the substrate, thus reducing stress and warpage in the final
product.
[0037] FIGS. 9A-9B depict another optical sensor package 101i. The
optical sensor package 101i includes a second layer of molding
compound 155 on the bottom side of the package. The second molding
compound 155 can be applied to the bottom side of the substrate
105, encapsulating solder balls 113 that can then be polished down
to reveal standard bond pad dimensions. Additionally, this allows
for the inclusion of a bottom mounted components, such as control
die 157, passive devices, and the like, which could result in a
smaller form factor and more cost effective package. Typically
OCEMC materials have relatively high coefficient of thermal
expansions (CTEs) compared to other materials used in the
construction of the package. The second layer of mold compound 155
can counteract unwanted effects (e.g., warpage, stress) of the high
CTE materials that cure at higher temps as the cool down to room
temp.
[0038] FIG. 10 depicts another optical sensor package 101j. The
optical sensor package 101j includes a reflecting surface 523
having a curved surface configured to reflect light emitted by the
LED light source 119 and direct this light to the sensing region.
The reflecting surface is incorporated into an encapsulant or
protective cover over the LEDs. The curved geometry may be used to
further tune the illumination provided. The curved reflecting
surface 523 may include a parabolic or elliptical shape, as two
examples. The parabolic reflecting surface can be used with the LED
light source 119 positioned at the focus of the parabola to provide
a highly collimated beam of light reflected from the surface 523
into the light guide.
[0039] FIG. 11 shows an example of an end use application of an
optical fingerprint sensor package 301. In FIG. 11, the optical
fingerprint sensor package 301 is placed under the cover glass 360
of a display, e.g., on a mobile device. The sensor package 301 is
attached to an underside of the cover glass 158 using an optically
clear adhesive (OCA) 159 allowing it to be optically coupled to the
cover glass 158. Also, this CMOS image sensor-based fingerprint
sensor package can also be mounted directly under a touchscreen,
which can enable coupling of touch screen functions with the
optical fingerprint sensor. The "under button" form factors are
also compatible with this package design.
[0040] With reference to FIG. 11, the optical fingerprint sensor
package 301 may be used to sense a fingerprint as follows. When a
finger 140 is present over the sensor, the LED light sources 119
emit light upwards towards the reflecting surface 123 of the
package. The reflecting surface 123 reflects all or a portion of
this light towards the sensing region where it can be affected by
the finger 140. In particular, if total internal reflection (TIR)
mode illumination is used, the reflecting surface 123 reflects the
light into a light guide positioned in a sensing area over the
image sensor die 103. The light guide may be provided by the
optical sensor package 301 itself, by the cover glass 158, or by a
combination thereof. The light in the light guide is affected by
the finger 140 in areas where the finger is in contact with an
upper surface of the cover glass 158. For example, contact from the
finger 140 may cause frustrated total internal reflection or
scattering of the light in the light guide, and direct this light
back down towards the image sensor die 103 below. This light then
passes through the light filter layer 117 before reaching the
photodetector elements of the image sensor die 103, where the light
filter 117 layer acts on the light to provide a suitable
fingerprint image capture by the image sensor die 103. A similar
operating mode may be achieved with cover layers other than the
cover glass 158 or with no cover layer at all, in which case an
upper surface of the sensor package could provide a sensing surface
for the finger. Also, other illumination modes, such as direct
illumination or non-TIR illumination modes may be used, in which
case the angle, shape, or positioning of the reflecting surface 123
may be adjusted accordingly to direct light to the appropriate
area. If a non-TIR illumination mode is used, then a light guide
need not be included in the package, or the light guide may be
replaced or enhanced with other features, such as a scattering
layer for extracting light.
[0041] FIGS. 12A-12B depict two process flows for construction of
optical sensor packages. FIG. 12A depicts a process flow 661a for
construction of a wire bonded solution. Manufacturing of some of
the individual components, such as the image sensor and light
filter 117 layer are omitted for clarity. At step 663, an image
sensor wafer is singulated or diced using a mechanical saw, laser,
or other means. Optionally, the image sensor wafer is provided with
a wafer level applied light filter and/or light guide layer. At
step 665, the individual image sensor dies are attached to a
substrate panel using a pick and place machine. At step 667, the
image sensor dies are electrically connected to the substrate panel
using wire bonding. At step 669, LEDs are surface mounted to the
substrate panel, in areas neighboring the image sensor dies. At
step 671, the LEDs are overmolded with an optically clear epoxy
molding compound. The optically clear epoxy molding compound can be
formed with a surface configured to reflect the light emitted from
the LEDs. The optically clear molding compound may optionally be
formed over all or a portion of the image sensor dies at this
stage. At step 673, a reflective film is deposited over the outer
surface of the optically clear epoxy mold compound, if desired. The
reflective film can be formed with windows over the active sensing
area of the image sensor dies at this stage. At step 675, the
substrate panel with the image sensor dies and over molded LEDs
attached thereto is singulated into a plurality of individual
optical sensors. At step 677, BGA or flexible circuit is attached
to the substrate and electrically connected thereto.
[0042] FIG. 12B depicts another process flow 661b for construction
of a flip chip solution. At step 663, an image sensor wafer is
singulated or diced using a mechanical saw, laser, or other means.
Optionally, the image sensor wafer is provided with a wafer level
applied light filter and/or light guide layer. At step 665, the
individual image sensor dies are flip chip attached to a substrate
panel using a pick and place machine. At step 681, underfill is
dispensed and cured. At step 669, LEDs are surface mounted to the
substrate panel, in areas neighboring the image sensor dies. At
step 671, the LEDs are overmolded with an optically clear epoxy
molding compound. The optically clear epoxy molding compound is
formed with a surface configured to reflect the light emitted from
the LEDs. The optically clear molding compound may optionally be
formed over all or a portion of the image sensor dies at this
stage. At step 673, a reflective film is deposited over the outer
surface of the optically clear epoxy mold compound, if desired. The
reflective film can be formed with windows over the active sensing
area of the image sensor dies at this stage. At step 675, the
substrate panel with the image sensor dies and over molded LEDs
attached thereto is singulated into a plurality of individual
optical sensors. At step 677, BGA or flexible circuit is attached
to the substrate and electrically connected thereto.
[0043] Various embodiments described herein may address one or more
of the following fundamental issues associated with the state of
the art approach to creating an optical fingerprint sensor
package:
[0044] (1) utilizing very mature molding processes and commercially
available optically clear molding compounds to simultaneously
protect the interconnects and/or active chip regions while also
creating a functional light guide in a cost effective manner;
[0045] (2) making use of all currently available image sensor types
(for example, lower cost front side illumination (F SI) type as
well as back side illumination (BSI) type CMOS image sensors can be
utilized);
[0046] (3) multiple die interconnect technologies can be employed
in this packaging process (for example, standard or low profile
wire bonding (e.g., as afforded by reverse bonding, to maximize top
side clearance) can be used, and flip chip technology (multiple
types) can also be employed to further reduce the form factor
(size) of the package;
[0047] (4) in order to take advantage of flip chip interconnect
processes, through silicon via technology (TSV) can be used to
route the signals to the back side of the die to allow for the
active side of the image sensor to face up with the interconnects
on the opposite side, and by using CMOS image sensors with this
interconnect technology, a smaller form factor device can be
realized;
[0048] (5) a novel mold design coupled with optical modeling allows
the use of molded in light guides (using OCEMC) to provide higher
performance at lower cost;
[0049] (6) an embodiment can be achieved by using wafer level
applied (can be laminated) optically clear illumination layer(s)
formed directly on top of a wafer level applied collimator/or other
light filter layer that may improve performance by reducing trapped
open spaces and providing better light guiding performance;
[0050] (7) reflector structures can be strategically placed to
enhance the light guide performance and can be overmolded using
OCEMC;
[0051] (8) a wafer level applied (can be laminated) low index of
refraction layer or a molded in air gap to improve the performance
of the sensor;
[0052] (9) all package types can use matrix molded processing such
that lower cost and higher volume can be achieved; and
[0053] (10) reflective films can be applied as needed post molding
to fine tune the optical properties of the final package
construction.
[0054] It will be appreciated that the various embodiments
described above can be modified in various ways, and various
features contained therein can be combined, modified, or removed in
various ways without departing from the scope and spirit of this
disclosure.
[0055] Thus, the embodiments and examples set forth herein were
presented in order to best explain the present disclosure and its
particular application and to thereby enable those skilled in the
art to make and use the various embodiments. However, those skilled
in the art will recognize that the foregoing description and
examples have been presented for the purposes of illustration and
example only. The description as set forth is not intended to be
exhaustive or to limit the embodiments to the precise form
disclosed. Those skilled in the art will also appreciate that
various features from different embodiments and examples set forth
herein may be combined, modified, and/or used together without
departing from the scope of the present disclosure.
* * * * *